This invention relates to the manufacture of flexible rubber tubing with annular or helical corrugations. More particularly, the invention relates to a unique variation of the method and apparatus for the manufacture of such tubing in accordance with U.S. Pat. Nos. 3,168,604, 3,304,581, 3,669,586 and/or 3,705,780, and especially to a variation thereof that is particularly advantageous in the manufacture of corrugated tubing with relatively thin walls, for example, with a wall thickness of around 0.04 in. For the purpose of this specification, the expression "circumferential" will be used to include both annular and helical convolutions.
As disclosed in U.S. Pat. Nos. 3,168,604, 3,304,581, 3,669,586 and 3,705,780, corrugated tubing with annular or helical corrugations may be made with external forming devices including axially spaced annular discs or helices that are employed with forming mandrels and air pressure means to produce embryonic corrugations in uncured rubber sleeves. Each time a tube is formed, the external forming device is placed over a forming mandrel (coated with a lubricant such as a silicone composition) on which a sleeve has been positioned, both the internal and external surfaces of the sleeve being supplied with a lubricant such as a silicone composition, and the sleeve is radially expanded so that it bulges into the spaces between the discs or turns of the helix to form creases between the bulges.
According to the aforesaid patents, the forming member and sleeve are then collapsed axially so that the sleeve is axially compressed, concertina-fashion. The creases together with adjacent bulges provide embryonic corrugations. Then the forming member is axially extended together with the sleeve after which the sleeve is removed from the forming mandrel and from within the forming member and placed on a cylindrical curing mandrel where it is axially foreshortened, concertina-fashion into a corrugated form with the desired spacing between adjacent annular or helical corrugations. The curing mandrel with the sleeve on it is then placed in an oven to cure the sleeve and set the corrugations.
The method and apparatus thus described have been used to produce flexible tubing of both circular and non-circular cross sectional form with either annular or helical corrugations. Such tubing is used to great advantage in many and various applications.
It will be apparent from the foregoing patents that the external forming member used to form the embryonic corrugations requires fabrication by skilled workers who must, in some instances, fabricate and weld the various parts together in an operation that may take several hours. Because many different sizes of tubing must be made, the fabrication of the forming members is a major factor in the overall cost of the tubing.
Also, since the external forming members of the prior art patents discussed above utilize metal parts with narrow edges that come into contact with the uncured rubber sleeve, a limitation is imposed on the wall thickness of the uncured rubber sleeves that may be used. The wall thickness and rubber hardness must be sufficient to resist cutting and penetration by the edges of the forming member during the operation of forming the embryonic corrugations and separating the forming member and the uncured sleeve. As a result of this, the aforesaid method and apparatus have been limited as to the thinness of the walls of tubing that can be manufactured. While greater wall thicknesses are desired for many applications, there are some instances where unusually small wall thicknesses are required--such as, for example, where the tubing is a throw-away type product where minimal cost is an important consideration. An example of such tubing is flexible tubing for gas connections used in medical applications.
The method and apparatus of the present invention, however, resolve the difficulties indicated above and afford other features and advantages heretofore not obtainable.